The present invention relates to the isolation and characterization of a novel gene relating to epilepsy. More specifically, the invention relates to the isolation and characterization of the Monogenic Audiogenic Seizure-susceptible gene, hereinafter mass1 gene.
Epilepsy is a common neurological disorder that affects nearly 2.5 million people in the United States. Epilepsy is characterized by recurrent seizures resulting from a sudden burst of electrical energy in the brain. The electrical discharge of brain cells causes a change in a person""s consciousness, movement, and/or sensations. The intensity and frequency of the epileptic seizures varies from person to person.
Epilepsies in humans can be separated into two forms, symptomatic and non-symptomatic. Symptomatic epilepsy is a seizure disorder related to a known cause such as metabolic disease, brain malformations, or brain tumors. In these cases, seizures presumably occur because of a very abnormal focus (or foci) in the brain. Genetic models of symptomatic epilepsy include the weaver mouse (wv), in which a mutation of the G protein-gated inwardly rectifying potassium channel GIRK2 results in neuro-developmental abnormalities and seizures. Signorini, S. et al. (1997), Proc Natl Acad Sci USA 94: 923-7. Fragile X-associated protein knock-out mice have a neurodevelopmental syndrome with lowered thresholds to audiogenic seizures. Musumeci, S. A. et al.(2000), Epilepsia 41: 19-23. Audiogenic seizures can also be induced in seizure-resistant mice such as C57BL/6 by repetitive sound stimulation, suggesting that seizure-susceptibility can be influenced by multiple genetic and environmental factors. Henry, K. R. (1967), Science 158: 938-40.
Non-symptomatic epilepsies are defined when no structural or metabolic lesions are recognized and the patients have no other neurological findings between seizures. This latter group of patients is more likely to have primary neuronal hyperexcitability that is not caused by metabolic, developmental or structural lesions. Molecular characterization of electrical hyperexcitability in human muscle diseases led to the hypothesis that such disorders might be the result of mutations in neuronal ion channels, the primary determinants of neuronal membrane excitability. Ptacek, L. J. et al. (1991), Cell 67: 1021-7.
All non-symptomatic human epilepsy syndromes and genetic mouse seizure models that have been characterized at a molecular level are caused by mutations in ion channels. Ptacek, L. J. (1999), Semin Neurol 19: 363-9; Jen, J. and L. J. Ptacek (2000), Channelopathies: Episodic Disorders of the Nervous System. Metabolic and Molecular Bases of Inherited Disease. C. R. Schriver, A. L. Beaudet, W. S. Sly and D. Valle. New York, McGraw-Hill. pp. 5223-5238; Noebels, J. L. (2000), The Inherited Epilepsies. Metabolic and Molecular Bases of Inherited Disease. C. R. Schriver, A. L. Beaudet, W. S. Sly and D. Valle. New York, McGraw-Hill. pp 5807-5832. Some patients with febrile seizures have been recognized to have mutations in sodium channel xcex1 and xcex21 subunits while some patients with epilepsy and episodic ataxia were shown to have calcium channel xcex2-subunit mutations. Wallace, R. H. et al. (1998), Nat Genet 19: 366-70; Escayg, A. et al. (2000), Am J Hum Genet 66: 1531-9; Escayg, A. et al. (2000), Nat Genet 24: 343-5. The voltage-gated potassium channel genes KCNQ2 and KCNQ3, when mutated, result in benign familial neonatal convulsions. Biervert, C. et al. (1998), Science 279: 403-6; Charlier, C. et al. (1998), Nat Genet 18: 53-5; Singh, N. A. et al. (1998), Nat Genet 18: 25-9. Ligand-gated channels can also result in epilepsy as demonstrated by mutations in the xcex14 subunit of the neuronal nicotinic acetylcholine receptor that result in autosomal dominant nocturnal frontal lobe epilepsy. Steinlein, O. K. et al. (1995), Nat Genet 11: 201-3. In mice, the xcex1, xcex2 and xcex3 subunits of the voltage-sensitive calcium channel have been associated with the tottering (tg), lethargic (lh) and stargazer (stg) models of absence seizures. Fletcher, C. F. et al (1996), Cell 87: 607-17; Burgess, D. L. et al. (1997), Cell 88: 385-92; Letts, V. A. et al. (1998), Nat Genet 19: 340-7. Finally, audiogenic seizure-susceptibility has been characterized in a mouse knockout model of the 5-HT2C receptor; homozygous mice have audiogenic seizures and altered feeding behavior. Tecott, L. H. et al. (1995), Nature 374: 542-6; Brennan, T. J. et al. (1997), Nat Genet 16: 387-90.
The Frings mouse represents one of many strains of mice and rats that are sensitive to audiogenic seizures (AGS). These AGS-susceptible rodents represent models of generalized reflex epilepsy and include the well-studied DBA/2 mouse and GEPR-9 rat. The Frings mouse seizure phenotype is similar to other described audiogenic seizes and is characterized by wild running, loss of righting reflex, tonic flexion and tonic extension in response to high intensity sound stimulation Schreiber, R. A. et al. (1980), Genet 10: 537-43. This strain was characterized 50 years ago when it arose as a spontaneous mutation on the Swiss Albino background. Frings, H. et al. (1951), J Mammal 32: 60-76. Selective inbreeding for seizure-susceptibility produced the current homozygous Frings strain with  greater than 99% penetrance of audiogenic seizures. The Frings mouse seizure phenotype was due to the autosomal recessive transmission of a single gene.
Audiogenic seizures have been observed in polygenic rodent models, such as the DBA/2 mouse and GEPR-9 rat. Collins, R. L. (1970), Behav Genet 1: 99-109; Seyfried, T. N. et al. (1980), Genetics 94: 701-718; Seyfried, T. N. and G. H. Glaser (1981), Genetics 99: 117-126; Neumann, P. E. and T. N. Seyfried (1990), Behav Genet 20: 307-23; Neumann, P. E. and R. L. Collins (1991), Proc Natl Acad Sci USA 88: 5408-12; Ribak, C. E. et al. (1988), Epilepsy Res 2: 345-55. While no genes associated with audiogenic seizures in spontaneous mutant models have been cloned, three putative loci associated with seizure-susceptibility in the DBA/2 mouse (asp1, asp2, and asp3) have been mapped to chromosomes 12, 4, and 7, respectively. Neumann and Seyfried, supra; Neumann, P. E. and R. L. Collins, supra. As a monogenic audiogenic seizures model, the Frings mice provided a unique opportunity for cloning and characterization of an audiogenic seizures gene. The Frings mice are an important naturally occurring monogenic model of a discrete non-symptomatic epilepsy and provide significant information on a novel mechanism of seizure-susceptibility as well as central nervous system excitability in general.
In light of the foregoing, it will be appreciated that it would be an advancement in the art to identify and characterize nucleic acid sequences that are associated with the monogenic AGS susceptibility in Frings mice. It would be a further advancement to identify and characterize the human orthologue of this gene. It would be a further advancement if the nucleic acid sequences could provide additional understanding of how epileptic seizures are triggered in disease. It would be a further advancement to provide a transgenic animal model wherein the endogenous gene associated with the Frings phenotype is mutated.
Such nucleic acid sequences and animals are disclosed and claimed herein.
The present invention relates to an isolated novel gene which has been imputed in audiogenic seizure-susceptibility in mice known as the mass1 gene. Provided herein are nucleic acid molecules that encode the MASS1 protein. The nucleic acid molecules of the present invention may also comprise the nucleotide sequence for human mass1 (SEQ ID NO: 3) and murine mass1 (SEQ ID NO: 1). In certain other embodiments, the present invention provides nucleic acid molecules that code for the amino acid sequence of human MASS1 (SEQ ID NO: 4) and murine MASS1 (SEQ ID NO: 2). The invention also provides nucleic acid molecules complementary to the nucleic acid molecules of SEQ ID NO: 3 and SEQ ID NO: 1. The invention also relates to other mammalian mass1 genes and MASS1 proteins.
The present invention also relates to an isolated nucleic acid having at least 15 consecutive nucleotides as represented by a nucleotide sequence selected from the nucleotides of the murine mass1 gene (SEQ ID NO: 1) and the nucleotides of the human mass1 gene (SEQ ID NO: 3). A nucleotide having in the range from about 15 to about 30 consecutive nucleotides as represented by a nucleotide sequence selected from the nucleotides of the murine mass1 gene (SEQ ID NO: 1) and the nucleotides of the human mass1 gene (SEQ ID NO: 3) is also within the scope of the present invention.
The present invention also provides recombinant vectors comprising nucleic acid molecules that code for MASS1. These recombinant vectors may be plasmids. In other embodiments, these recombinant vectors are prokaryotic or eukaryotic expression vectors. The nucleic acid coding for MASS1 may also be operably linked to a heterologous promoter. The present invention further provides host cells comprising a nucleic acid that codes for MASS1.
The present invention also relates to a transgenic mammal with a mutation in one or both alleles of the endogenous mass1 gene. The mutation in one or both of the endogenous mass1 genes may result in a mammal with a seizure-susceptible phenotype. The transgenic mammal of the present invention may be a mouse. The mutation may result from the insertion of a selectable marker gene sequence or other heterologous sequence into the mammal""s genome by homologous recombination. The invention also provides cells derived from the transgenic mammal.
These and other advantages of the present invention will become apparent upon reading the following detailed description and appended claims.